Method for discriminating anodal and cathodal capture

ABSTRACT

An implantable device and associated method detect anodal capture during electrical stimulation. A first pacing pulse is delivered using a first cathode and a first anode. A second pacing pulse is delivered using the first cathode and a second anode. A first response to the first pacing pulse and a second response to the second pacing pulse are measured. Anodal capture of the first pacing pulse at the first anode is detected in response to a first difference between the first response and the second response.

TECHNICAL FIELD

The disclosure relates generally to medical devices for deliveringelectrical stimulation and, in particular, to an apparatus and methodfor discriminating between anodal and cathodal capture in an electricalstimulation therapy device.

BACKGROUND

In site-specific cardiac pacing methods, such as cardiacresynchronization therapy (CRT), cathodal stimulation is generallydesired. In some cases, an anodal capture threshold may be lower thanthe cathodal capture threshold. As a result, a clinician may think thatcapture of a particular heart chamber is occurring at the cathodeelectrode site when in fact the evoked response is initiated at theanode electrode site. This change in activation sequence from anexpected activation sequence of the heart may result in less benefitfrom a delivered therapy than intended or possible. This compromisedtherapeutic benefit may go unrecognized since the clinician willtypically not realize that anodal capture is occurring instead ofcathodal capture.

In particular, as multi-polar coronary sinus leads become commerciallyavailable for pacing and sensing in the left ventricle, anodal capturein the left ventricle can become a more common occurrence when a bipolarpair of electrodes positioned along the left ventricle is selected forpacing in the left ventricle. In CRT, anodal stimulation in the LV willresult in a different activation sequence of the LV than expected.Doctors will typically select a cathode positioned at a desired pacingsite, such as the near the LV base, paired with an anode that results inthe lowest capture threshold to conserve pacemaker battery energy. Insome cases, the selected anode may cause anodal capture only or acombination of anodal and cathodal capture. If the anode is nearer theLV apex than the base, less desired apical pacing will occur, unknown tothe clinician.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an implantable medical device (IMD) coupled to apatient's heart by way of a right ventricular (RV) lead and a coronarysinus (CS) lead.

FIG. 2 is a functional block diagram of the IMD shown in FIG. 1.

FIG. 3 is a flow chart of a method for selecting electrodes fordelivering a pacing therapy.

FIG. 4A is a flow chart of a method for detecting anodal capture in theleft ventricle according to one embodiment.

FIG. 4B is a schematic drawing depicting one configuration for makingmeasurements during an anodal capture analysis algorithm.

FIG. 4C is a schematic drawing depicting another configuration formaking measurements during an anodal capture analysis algorithm.

FIG. 5 is a flow chart of a method for detecting anodal captureaccording to an alternative embodiment.

FIG. 6 is a flow chart of a method for discriminating between anodal andcathodal capture according to yet another embodiment.

FIG. 7 is a flow chart of a method for performing anodal captureanalysis and reporting results according to one embodiment.

FIG. 8 is a schematic diagram of a configuration for detecting anodalcapture during bipolar pacing using evoked response sensing.

FIG. 9 is a flow chart of a method for detecting anodal capture duringbipolar pacing using evoked response sensing at both the candidatecathode and anode as generally depicted in the configuration of FIG. 8.

FIG. 10 is a flow chart of a method for detecting and discriminatinganodal, cathodal and simultaneous anodal and cathodal capture duringbipolar pacing.

DETAILED DESCRIPTION

In the following description, references are made to illustrativeembodiments. It is understood that other embodiments may be utilizedwithout departing from the scope of the disclosure. As used herein, theterm “module” refers to an application specific integrated circuit(ASIC), an electronic circuit, a processor (shared, dedicated, or group)and memory that execute one or more software or firmware programs, acombinational logic circuit, or other suitable components that providethe described functionality.

Methods and associated circuitry are described herein for detecting anddiscriminating anodal stimulation during bipolar stimulation of a heartchamber. These methods may be implemented in any single, dual, ormulti-chamber pacing device having at least two electrodes positionedfor bipolar pacing in a heart chamber. More often, practice of thedisclosed methods will be used when multiple electrodes are available ina paced heart chamber providing two or more bipolar electrode vectors tochoose from for pacing in the heart chamber. In some embodiments, atleast one electrode positioned away from the heart chamber is providedfor use as an anode for obtaining measurements during unipolar pacing ofthe heart chamber that are used for discriminating between anodal andcathodal capture. The anode electrode may be in or along another heartchamber, along the housing of an associated IMD, or a subcutaneouslyimplanted electrode such as a patch electrode. In some embodiments,which involve measuring conduction times between heart chambers,electrodes for sensing a conducted depolarization in a heart chamberother than the one being paced are needed. In other embodiments, adistant sensing bipole may be used to measure a conduction time withinthe same chamber being paced.

In the following description, a dual-chamber (biventricular) pacingdevice is described as one illustrative embodiment of a device that mayutilize the anodal capture detection methods described herein. Thisdevice is used in particular for delivering cardiac resynchronizationtherapy (CRT) by pacing in one or both ventricles. It should berecognized, however, that anodal capture detection and discriminationduring bipolar pacing may be implemented in numerous deviceconfigurations that include bipolar pacing capabilities in at least oneheart chamber for delivering CRT or any other pacing therapy.Furthermore, aspects of the anodal capture detection and discriminationmethods may be implemented in any medical device delivering electricalstimulation to excitable body tissue and are not necessarily limited topractice in cardiac pacing applications.

FIG. 1 depicts an implantable medical device (IMD) 10 coupled to apatient's heart 8 by way of a right ventricular (RV) lead 16 and acoronary sinus (CS) lead 18. The IMD 10 is embodied as a cardiac pacingdevice provided for restoring ventricular synchrony by delivering pacingpulses to one or more heart chambers as needed to control the heartactivation sequence. The heart 8 is shown in a partially cut-away viewillustrating the upper heart chambers, the right atrium (RA) and leftatrium (LA), and the lower heart chambers, the right ventricle (RV) andleft ventricle (LV), and the great cardiac vein 48, which branches toform inferior cardiac veins. The great cardiac vein 48 opens into thecoronary sinus (CS) in the right atrium.

The transvenous leads 16 and 18 connect IMD 10 with the RV and the LV,respectively. It is recognized that in some embodiments, additionalleads and/or electrodes may be coupled to an IMD for connecting the IMDwith the RA and the LA to provide sensing and/or pacing in three or allfour chambers of the heart.

Each lead 16 and 18 carries pace/sense electrodes coupled to insulated,elongated conductors extending through leads 16 and 18. A remoteindifferent housing electrode 12 is formed as part of the outer surfaceof the housing of the IMD 10. The pace/sense electrodes and the remoteindifferent housing electrode 12 can be selectively employed to providea number of unipolar and bipolar pace/sense electrode combinations forpacing and sensing functions.

RV lead 16 is shown as a transvenous, endocardial lead passed throughthe RA into the RV. The RV lead 16 is formed with a proximal leadconnector adapted for insertion into a connector bore of IMD connectorblock 14. The lead connector (not shown in FIG. 1) electrically coupleselectrodes 20, 22, 24, and 26 carried by RV lead 16 to internalcircuitry of IMD 10 via connector block 14. RV pace/sense tip electrode20 and proximal RV pace/sense ring electrode 22 are provided for RVpacing and sensing of RV EGM signals. RV lead 16 additionally carries anRV coil electrode 24 and a superior vena cava (SVC) coil electrode 26,which may be used for delivering high-voltage cardioversion ordefibrillation shocks. RV ring electrode 22, RV coil electrode 24 or SVCcoil electrode 26 are used in some embodiments as an anode paired withan electrode positioned along the LV for delivering unipolar pacingpulses in the LV during anodal capture analysis.

In the illustrative embodiment, a multi-polar LV CS lead 18 is passedthrough the RA, into the CS and further into a cardiac vein 48 to extendthe distal four pace/sense electrodes 30, 32, 34 and 36 along the LVchamber to achieve LV pacing and sensing of LV EGM signals using anycombination of electrodes 30 through 36. The LV CS lead 18 is coupled ata proximal end lead connector (not shown) inserted into a bore of IMDconnector block 14 to provide electrical coupling of electrodes 30through 36 to IMD internal circuitry.

The depicted positions of the leads and electrodes shown in FIG. 1 in orabout the right and left ventricles are approximate and merelyillustrative. It is recognized that alternative leads and pace/senseelectrodes that are adapted for placement at pacing or sensing sites onor in or relative to the RA, LA, RV and/or LV may be used in conjunctionwith the methods described herein. For example, in a three chamberpacing device, a RA lead may be positioned carrying a tip and ringelectrode for pacing and sensing in the right atrial chamber.Additionally, in a four chamber embodiment, LV CS lead 22 could bearproximal LA CS pace/sense electrode(s) positioned along the lead body tolie adjacent the LA for use in pacing the LA or sensing LA EGM signals.A multi-chamber device in which anodal capture detection methods may bepracticed is generally disclosed in U.S. Pat. No. 7,555,336 (Sheth, etal.), hereby incorporated herein by reference in its entirety.

The electrodes designated above as “pace/sense” electrodes can generallybe used for both pacing and sensing functions. These “pace/sense”electrodes can be selected to be used exclusively as pace or senseelectrodes or to be used for both pacing and sensing in programmedcombinations for sensing cardiac signals and delivering cardiacstimulation pulses along selected sensing and pacing vectors. Separateor shared indifferent pace and sense electrodes can also be designatedin pacing and sensing functions, including the use of RV coil electrode24 and/or SVC coil electrode 26 as a pacing anode.

FIG. 2 is a functional block diagram of IMD 10. IMD 10 generallyincludes timing and control circuitry 52 and an operating system thatmay employ microprocessor 54 or a digital state machine for timingsensing and therapy delivery functions in accordance with a programmedoperating mode. Microprocessor 54 and associated memory 56 are coupledto the various components of IMD 10 via a data/address bus 55.Microprocessor 54, memory 56, timing and control 52, and captureanalysis module 80 may operate cooperatively as a controller forexecuting and controlling various functions of IMD 10.

IMD 10 includes therapy delivery module 50 for delivering a therapy inresponse to determining a need for therapy based on sensed physiologicalsignals. Therapy delivery module 50 provides electrical stimulationtherapies, such as cardiac pacing or arrhythmia therapies, includingCRT. Therapies are delivered by module 50 under the control of timingand control 52. Therapy delivery module 50 is typically coupled to twoor more electrodes 68 via an optional switch matrix 58. Switch matrix 58may be used for selecting which electrodes and corresponding polaritiesare used for delivering electrical stimulation pulses. Electrodes 68 maycorrespond to the electrodes shown in FIG. 1 or any electrodes coupledto IMD 10.

Therapy delivery module 50 includes an electrical pulse generator forgenerating pacing pulses. Timing and control 52, in cooperation withmicroprocessor 54 and capture analysis module 80, control the deliveryof pacing pulses by therapy delivery 50 according to a capture analysisalgorithm for detecting and discriminating anodal capture. The detectionof anodal capture is used to select which of electrodes 68 andcorresponding polarities are used in delivering a cardiac pacingtherapy.

Electrodes 68 are also used for receiving cardiac electrical signals.Cardiac electrical signals may be monitored for use in diagnosing ormonitoring a patient condition or may be used for determining when atherapy is needed and in controlling the timing and delivery of thetherapy. When used for sensing, electrodes 68 are coupled to signalprocessing circuitry 60 via switch matrix 58. Signal processor 60includes sense amplifiers and may include other signal conditioningcircuitry and an analog-to-digital converter. Cardiac EGM signals(either analog sensed event signals or digitized signals or both) maythen be used by microprocessor 54 for detecting physiological events,such as detecting and discriminating cardiac arrhythmias, determiningactivation patterns of the patient's heart, and in performing anodalcapture analysis as will be described further herein.

IMD 10 may additionally be coupled to one or more physiological sensors70. Physiological sensors 70 may include pressure sensors,accelerometers, flow sensors, blood chemistry sensors, activity sensorsor other physiological sensors for use with implantable devices.Physiological sensors may be carried by leads extending from IMD 10 orincorporated in or on the IMD housing 12. Sensor interface 62 receivessignals from sensors 70 and provides sensor signals to signal processingcircuitry 60. Sensor signals are used by microprocessor 54 for detectingphysiological events or conditions.

The operating system includes associated memory 56 for storing a varietyof programmed-in operating mode and parameter values that are used bymicroprocessor 54. The memory 56 may also be used for storing datacompiled from sensed signals and/or relating to device operating historyfor telemetry out upon receipt of a retrieval or interrogationinstruction. A capture analysis algorithm may be stored in memory 56 andexecuted by microprocessor 54 and/or capture analysis module 80 withinput received from electrodes 68 for detecting anodal capture.Alternatively, capture analysis module 80 may be embodied as dedicatedcircuitry for receiving and processing signals for detecting anodalcapture and generating a report or warnings pertaining to anodalcapture. Microprocessor 54 may respond to capture analysis data byaltering electrode selection for delivering a cardiac pacing therapy ortriggering alert 74 to generate an alert signal or message to aclinician that anodal capture is occurring. Data relating to captureanalysis may be stored in memory 56 for later retrieval.

IMD 10 further includes telemetry circuitry 64 and antenna 65.Programming commands or data are transmitted during uplink or downlinktelemetry between IMD telemetry circuitry 64 and external telemetrycircuitry included in a programmer or monitoring unit. Telemetrycircuitry 64 may be used to transmit an alert or notification generatedin response to detecting anodal capture.

FIG. 3 is a flow chart of a method for selecting electrodes fordelivering a pacing therapy based at least in part on the detection ofanodal capture. Flow chart 100 and other flow charts presented hereinare intended to illustrate the functional operation of the device, andshould not be construed as reflective of a specific form of software orhardware necessary to practice the methods described. It is believedthat the particular form of software, hardware and/or firmware will bedetermined primarily by the particular system architecture employed inthe device and by the particular detection and therapy deliverymethodologies employed by the device. Providing circuitry to accomplishthe described functionality in the context of any modern IMD, given thedisclosure herein, is within the abilities of one of skill in the art.

Methods described in conjunction with flow charts presented herein maybe implemented in a computer-readable medium that includes instructionsfor causing a programmable processor to carry out the methods described.A “computer-readable medium” includes but is not limited to any volatileor non-volatile media, such as a RAM, ROM, CD-ROM, NVRAM, EEPROM, flashmemory, and the like. The instructions may be implemented as one or moresoftware modules, which may be executed by themselves or in combinationwith other software.

At block 102, a bipolar pair of pacing electrodes is selected fordelivering a cardiac pacing in a heart chamber. Detection of anodalcapture is described herein with regard to detecting anodal capture inthe left ventricle during bipolar pacing of the left ventricle. It isrecognized that detection of anodal capture during bipolar pacing inanother heart chamber, or in another body location, may be performedusing the methods described herein. In the illustrative embodiment, abipolar pair of electrodes is selected from a multi-polar LV CS leadsuch as lead 18 shown in FIG. 1. LV pacing is delivered at block 104according to a capture analysis algorithm to detect whether anodalcapture is occurring in the LV at block 106. The LV pacing at block 104may involve both unipolar and bipolar pacing in the LV for makingvarious measurements for detecting anodal capture during bipolar pacing.

If anodal capture is detected, a notification may be generated to aclinician at block 108. The clinician, made aware that anodal capture isoccurring, may program the IMD to use a different pacing electrode pairfor pacing in the LV.

Additionally or alternatively, a different LV pacing bipole may beselected automatically at block 110. For example, a different electrodemay be selected as an anode with the same cathode, located at a desiredLV pacing site, in an attempt to obtain cathodal stimulation at thedesired pacing site. A different anode selected at block 110 may bewithin the LV or in another heart chamber, for example, an RV electrode,or the housing of the IMD in order to minimize the likelihood of anodalcapture in the LV. Selection of a different electrode pair may involveselecting a different anode only, a different cathode only, or adifferent anode and a different cathode to achieve cathodal capture at adesired pacing site. If anodal capture is not detected at block 106, LVpacing can be delivered using the selected electrode pair at block 112.

FIG. 4A is a flow chart 200 of one method for detecting anodal capturein the LV. At block 202, an anodal capture test is initiated. The anodalcapture test may be performed upon command or automatically and may beperformed alone or in combination with a capture threshold test. Theanodal capture test may be performed automatically on a periodic basisor in response to detecting a change in a physiological signal, e.g. aworsening hemodynamic signal.

At block 204, an LV pacing cathode is selected and LV pacing isdelivered between the LV cathode electrode and a “universal” anode. TheLV pacing cathode is a candidate pacing cathode being evaluated for thelikelihood of anodal capture if the cathode were to be used fordelivering a pacing therapy. The “universal” anode is an anode electrodethat will be used to measure both a control and test pacing responseduring evaluation of a given cathode electrode for the presence ofanodal capture. A “universal” anode may be positioned away from the LV,such as an RV ring electrode 22, RV coil electrode 24, SVC coilelectrode 26, or an electrode located away from the heart, such as ahousing electrode 12 formed along the IMD housing, all shown in FIG. 1.

For any of these anode selections, the pacing delivered at block 204will be unipolar pacing. As used herein, the term “unipolar pacing”refers to pacing using one electrode positioned in or along the heartchamber to be paced and one electrode positioned away from the heartchamber being paced, either in another heart chamber or away from theheart. In one embodiment, unipolar LV pacing is delivered at block 204between a selected LV cathode electrode and any available electrodepositioned away from the LV, which may be in or along another heartchamber, the SVC, the IMD housing, any subcutaneous location, or otherlocations that are not in or along the LV.

In another embodiment, the “universal” anode may be another electrode inthe heart chamber being paced, i.e. the same chamber as the cathodeelectrode. Examples measurement configurations that include a“universal” anode located away from the paced chamber and a “universal”anode located in the paced chamber will be described in conjunction withFIGS. 4B and 4C.

In a quadripolar LV lead such as lead 22 shown in FIG. 1, the electrodes30, 32, 34, and 36 may be referred to as LV1, LV2, LV3 and LV4,respectively, moving from the most distal LV1 electrode 30 to the mostproximal LV4 electrode 36. The most proximal LV4 electrode 36 may bepositioned along the LV base and may be the most desirable cathodeelectrode for delivering LV basal pacing.

As such, in one example, the LV4 electrode 36 may be selected at block204 as a pacing cathode in a unipolar LV pacing vector using anyavailable electrode away from the LV as the anode. For example, duringthe anodal capture analysis algorithm, pacing is delivered between theLV4 electrode 36 (or other selected LV cathode electrode) and an RVelectrode, such as RV coil electrode 24 (FIG. 1), serving as the anode.

The time interval between the pacing pulse and an RV depolarizationsensed after the LV pacing pulse is measured at block 206 as a controlconduction time (CT). Here, and in other embodiments of anodal captureanalysis algorithms presently disclosed, when pacing pulses are beingdelivered to measure a response to the pacing pulses, the pulses aredelivered at time intervals that avoid interference of intrinsicdepolarizations with the measured response to a pacing pulse. Forexample, pacing pulses are delivered at a time interval that is shorterthan intrinsic RV depolarization arising from conduction from the atriato avoid intrinsic depolarization signals from interfering with CTmeasurements in the RV. Additionally, premature ventricular contraction(PVC) detection may be employed to avoid measuring a conducted PVC as aconducted depolarization response to the LV pacing pulse. Methods forcontrolling the timing of test pulses during a capture analysisalgorithm and for dealing with the occurrence of PVCs may correspondgenerally to methods disclosed in U.S. Patent Publication No.2010/0137935 (Parikh, et al.), hereby incorporated herein by referencein its entirety.

In practice, the pacing pulse amplitude delivered at block 204 may beset to a value just above the capture threshold. The conduction time ofa pacing-evoked depolarization from the LV to the RV can decrease withhigher pacing voltage. To provide comparable CT intervals measured usingdifferent electrode vectors, a consistent pacing pulse amplitude andpulse width relative to a measured capture threshold for a given pacingvector may be used when measuring an LVpace to RVsense CT. For example,a fixed increment above the capture threshold such as about 0.5 Vgreater than a measured capture threshold, may be used.

The RV EGM signal used for sensing an RV depolarization conducted fromthe LV may be sensed using the RV tip and ring electrodes 20 and 22. Inthis embodiment, it is assumed that cathodal capture is occurring in theLV and anodal capture is not occurring at the “universal” anode when thecontrol CT is measured. For example, for an LV-RVcoil pacingconfiguration used for measuring a control response to an LV pacingpulse, capture is occurring in the LV and is not occurring at the RVcoil.

Measuring the relative time of a conducted depolarization (R-wave)relative to an LV pacing pulse may involve measuring the time to anR-wave sense amplifier output. Sensing an R-wave in the RV may beperformed using a sense amplifier and auto-adjusting threshold asgenerally described in U.S. Pat. No. 5,117,824 (Keimel, et al.), herebyincorporated herein by reference in its entirety. In an alternativeembodiment, measuring the CT of the conducted RV depolarization relativeto an LV pacing pulse may involve analog-to-digital conversion of anventricular EGM signal and analysis of the digitized EGM signal todetermine a local activation time at a sensing bipole located a distancefrom the pacing cathode. The local activation time may be identified asany fiducial point along the R-wave of the EGM signal, such as amaximum, minimum, peak dV/dt, zero-crossing or other signal feature.

At block 208, a bipolar pair is selected in the LV using the same LVcathode electrode as used to measure the control CT. Any other availableLV electrode is selected as the anode in a candidate bipolar pacingvector for use during subsequent therapy delivery. Bipolar LV pacing isdelivered using the selected LV cathode and anode. The CT between the LVpacing pulse and a conducted depolarization is measured at block 210 asthe bipolar CT. The bipolar LV pacing pulse is delivered just above thecapture threshold, for example, a consistent fixed increment above thecapture threshold, to provide comparable time interval measurementsbetween pacing vectors with minimized influence of the pacing pulseamplitude on the measured conduction times. It is noted that, while itis known that some type of capture is occurring at the capturethreshold, it remains unknown whether that capture is occurring at theanode, cathode, or a combination of both.

At block 211, the polarity of the LV anode used during bipolar LV pacingis switched to a cathode and then used to deliver LV pacing with thesame “universal” anode electrode used during measurement of the controlCT. A test CT is measured at block 211 to obtain a CT corresponding tocapture at the candidate bipolar LV anode site. This test CT measuredduring LV pacing at the candidate bipolar anode site, i.e. using thecandidate bipolar anode as a cathode during pacing with the “universal”anode, gives an estimate of the CT that would be expected if anodalcapture is occurring during LV bipolar pacing using the candidate LVbipole.

At block 212, the bipolar CT is compared to the control CT and the testCT to determine if the bipolar CT approximately matches the control CT.If cathodal capture is occurring during pacing with the candidatebipole, the bipolar CT should approximately match the control CT. Ifanodal is capture is occurring during pacing with the candidate bipole,the bipolar CT should approximately match the test CT. As such, in oneembodiment the absolute difference between the candidate bipolar CT andthe control CT is compared to the absolute difference between thecandidate bipolar CT and the test CT. If the absolute difference betweenthe candidate bipolar CT and the control CT is less than the absolutedifference between the candidate bipolar CT and the test CT (a negativeresult at block 212), the candidate cathode being evaluated (LV4 in theabove example) is capturing.

If the bipolar CT is closer to the test CT than the control CT, theanode LV1 in this example is likely capturing. In an alternativeembodiment, the test CT may not be measured if the bipolar CT closelymatches the control CT within a predefined range, e.g. withinapproximately 10 ms of the control CT. In some cases, if the LV bipoleelectrodes are very close together, the conduction times from cathodaland anodal stimulation may not be separable. However, in this case, theimpact of pacing from the anode vs. pacing from the cathode duringbipolar pacing may have no clinical impact and therefore suchdiscrimination may be unnecessary.

If cathodal capture is occurring, the bipolar CT will be closer to thecontrol CT as determined at decision block 212. Cathodal capture isdetected at block 220. The selected candidate LV bipole can be used todeliver LV pacing pulses according to a programmed pacing therapy atblock 220. If the candidate bipolar CT is not closer to or does notapproximately match the control CT, anodal capture is detected at block214. A notification of anodal capture may be generated at block 214,and/or a different LV bipolar pair may be selected for evaluation byproceeding to block 216.

If other LV electrodes are available for use as an anode, as determinedat block 216, a new candidate bipolar pair using the same cathode and adifferent anode may be selected at block 218. A bipolar CT is measuredagain at block 210 using the same LV cathode electrode with a newlyselected LV anode electrode and the process continues to block 211.

If all available LV electrodes have been tested as an anode paired withthe currently selected LV cathode and resulted in anodal capturedetection, the process may return to block 204 to select a different LVelectrode as a new candidate cathode and repeat the anodal capture testuntil a suitable LV bipolar pair is identified that does not result inanodal capture. This process of selecting new candidate bipolarelectrode pairs for testing may be a fully automated process or may besemi-automated in which a user responds to a warning of anodal capturedetection and selects what actions will be taken next, for example,accept the electrode configuration, select a new anode, select a newcathode, select a new anode and new cathode, perform additionalmeasurements or the like.

In some instances, the control CT and the test CT may be equal. In thissituation, a different distant bipole may be selected for sensing aconducted depolarization for measuring the CTs in an attempt to obtaindistinct control and test CTs. Alternatively, a different method fordiscriminating between anodal and cathodal capture may be selected, suchas using a different measured response to the pacing pulse, for exampleevoked response timing or morphology as described below. In anotherembodiment, if the control and test CTs are equal, the algorithm may bestopped, and an inconclusive test may be reported.

FIG. 4B is a schematic drawing depicting one configuration 250 formaking measurements during an anodal capture test algorithm. In theschematic drawing, electrodes 251, 252, 253, and 254 are positionedalong or in a cardiac chamber to be paced, e.g. along the LV. It isrecognized that during therapy delivery, pacing may be delivered in oneor more heart chambers, not just the chamber being paced during theanodal capture analysis. Electrodes 255 and 256 are positioned away fromthe paced chamber, e.g. in the RV. Electrode 255, which may be a ring orcoil electrode, is shown to be used as a universal anode with any ofelectrodes 251 through 254 during unipolar pacing. In an illustrativeexample according to the method described in conjunction with FIG. 4A, acontrol measurement is made during unipolar pacing between electrode 251(candidate cathode) and electrode 255 (universal anode), along pacingvector 260 (with the cathodal to anodal polarities indicated by therespective letters “C” and “A”).

A control measurement made during this unipolar pacing may be the CTfrom the pacing cathode 251 to an R-wave sensed at a local site usingbipolar sensing electrodes in another heart chamber, such as electrodes256 and 255 which may correspond to RV tip and ring electrodes. Anybipole located a distance away from the cathode electrode can be used tomeasure a control CT.

A bipolar measurement is made during bipolar pacing between electrode251 (candidate cathode) and electrode 254 (anode) along vector 262. Withcontinued reference to the example given above, a bipolar CT may bemeasured by sensing a local R-wave at the bipole formed by electrodes255 and 256. If cathodal capture is occurring at candidate cathode 251,the control CT and the bipolar CT are expected to be similar because theconduction time of an evoked response occurring at electrode 251 to thedistant bipole electrodes 255 and 256 should be similar in both cases.

The anode electrode 254 of the pacing bipole is switched to a cathodepolarity, as indicated by the “C” and “A” notations, to measure a testresponse during unipolar pacing between electrode 254 (now a cathode)and the universal anode 255 along vector 264. Notice the reversedpolarity annotation for electrode 254 from A along vector 262 to C alongvector 264 highlighted by dashed circle. The cathode (C) and anode (A)polarities are indicated along vector 264. A test CT is measured at thedistant bipolar sensing electrodes 255 and 256. When the bipolar CTmeasured during pacing along vector 262 more closely matches the test CTmeasured during pacing along vector 264 than the control measurementmade during pacing along vector 260, anodal capture at electrode 254during bipolar pacing is detected or suspected.

The measured response to a pacing pulse during the anodal capture testmay be a CT between the paced heart chamber and another heart chamber asmeasured by determining the relative time of a locally sensed R-wave (orP-wave if pacing and sensing in the atria) and the preceding pacingpulse. The measurement of a response to a pacing pulse may include othermeasurements such as a capture threshold measurement, a measurementrelating to an evoked response detected in the paced chamber, or anycombination thereof, examples of which will be further described below.

In FIG. 4C, another configuration 270 for measuring pacing responses foranodal capture detection is depicted schematically. The electrodes 251,252, 253 and 254 are electrodes positioned in the heart chamber to bepaced, such as the LV, during the anodal capture analysis algorithm. Inthis case, electrodes in the chamber being paced are the only electrodesused during the anodal capture analysis test. This method can beperformed, for example in a single-chamber pacing application.

A bipolar measurement is made during pacing along a desired bipolarpacing vector 262 between electrode 251 (candidate cathode) andelectrode 254 (anode). A control measurement may be made in this caseduring pacing along another bipolar vector 272 between electrode 251(candidate cathode) and another electrode 252 (universal anode) in thesame heart chamber. A test measurement is made during pacing alongvector 274. The anode electrode 254 used during the bipolar measurementis switched to a cathode electrode, and pacing is delivered using thesame universal anode electrode 252 as the control measurement. In otherwords, anode electrode 252 is used as a universal anode for all controland test measurements made when evaluating a particular candidatecathode electrode 251. This universal anode 252 replaces the need for ananode (e.g. anode 255 in FIG. 4B) positioned away from the chamber beingpaced during anode capture analysis.

If the response to the pacing pulses is measured as a CT, the CT ismeasured by determining the relative time from the delivered pacingpulse and a locally sensed R-wave at a sensing bipole in the chamberbeing paced. In the example shown, electrodes 252 and 253 may beutilized as a sensing bipole for sensing a local R-wave and determininga CT. A sensing bipole may alternatively be an independent pair ofelectrodes located anywhere along the paced chamber. If the bipolar CTmeasured during pacing along vector 262 is closer to the test CT(meausured during pacing along vector 274 with electrode 254 as thecathode) than the control CT measured during pacing along vector 272,anodal capture is detected or suspected. The conducted R-wave isexpected to arrive at the sensing electrodes 252 and 253 atapproximately the same time if cathodal capture is occurring atelectrode 251 during pacing along vectors 262 and 272. If not, andparticularly if the test CT is closer to the control CT, capture islikely happening at anode 254 during bipolar pacing along vector 262.

FIG. 5 is a flow chart 300 of a method for detecting anodal captureaccording to an alternative embodiment. At block 302, an anodal capturetest is initiated. An LV cathode electrode is selected at block 304, andLV pacing is delivered using the candidate LV cathode electrode and auniversal anode electrode, which may be located away from the LV, suchas the RV coil electrode, such that the pacing is delivered in aunipolar manner. At block 306, the capture threshold for the selected LVcathode and anode is determined. The pacing pulse amplitude is varieduntil the capture threshold is identified according to a capturethreshold test. A capture threshold test is generally described in U.S.Pat. No. 5,873,898 (Hemming, et al.), hereby incorporated herein byreference in its entirety, however other capture threshold measurementmethods may be implemented.

The control CT is measured at block 308 as described previously. Thisprocess of measuring a capture threshold and a control CT is repeatedfor all available LV electrodes evaluated as candidate LV cathodespaired one at a time with a universal anode positioned away from the LVas indicated by blocks 310 and 312. The capture threshold data for eachcandidate LV electrode used as a cathode with an anode located outsidethe LV is stored in memory along with the corresponding control CT. This“control” data associated with LV cathodal capture during unipolar LVpacing is used in detecting LV anodal capture during LV bipolar pacingusing the candidate LV cathodes and various LV anodes.

At block 314, an LV bipolar pair is selected for delivering LV pacing.In one embodiment, a candidate LV bipole is selected based on a desiredpacing site during therapy delivery and/or the lowest capture thresholdmeasured at block 306. During LV bipolar pacing only (i.e., no pacing inthe RV), the bipolar CT is measured at block 320. The bipolar CT ismeasured during bipolar pacing using the candidate bipole at the samedistant sensing bipole as used to measure the control CT.

The bipolar CT is compared to the control CT at block 322. Anapproximate match detected at block 322 may be defined as a bipolar CTthat is closer to the control CT than to a test CT. The test CT ismeasured previously at block 304 during cathodal pacing at the candidatebipole anode site. A comparison of the absolute differences between thebipolar CT and control CT and the bipolar CT and the test CT asdescribed previously may be used at block 322 to determine anapproximate match between the bipolar CT and the control CT.

If the bipolar CT approximately matches or is closer to the control CTthan the test CT, cathodal capture is presumed. Anodal capture is notdetected. Cathodal capture may be reported at block 324, and/or LVpacing is delivered at block 324 using the selected LV bipole.

If the bipolar CT does not approximately match the control CT, anodalcapture is suspected as indicated at block 326. The measured bipolar CTmay be substantially longer or shorter than the control CT.

To determine if anodal capture is occurring, an additional response tothe bipolar pacing is measured and compared to a control and/or testresponse to LV pacing, where the control response uses the candidatecathode and a “universal” anode and the test response using the anode ofthe candidate bipolar pair switched to a cathode polarity. In theembodiment of FIG. 5, the additionally measured response is the capturethreshold.

A capture threshold measurement is performed at block 328 to determinethe capture threshold for the candidate LV bipole. The bipolar capturethreshold is referred to as threshold1. If the LV cathode of thecandidate LV bipolar pair is capturing, the bipolar capture threshold isexpected to be similar to the control capture threshold, when thecathode is used with a “universal” anode, such as the RV coil.

The cathode and anode polarity of the selected electrode pair isswitched at block 330, and a second LV bipolar capture threshold,referred to as threshold2, is measured at block 332, for this oppositepolarity of the candidate LV bipole electrodes. This switched polaritycapture threshold provides a “test” response because it provides anexpected capture threshold when capture is occurring at the anode of thecandidate bipolar pair.

Threshold1 is compared to the control capture threshold and the testcapture threshold (theshold2) at block 334. If the LV capture threshold1is closer to the test threshold2 than it is to the control capturethreshold, anodal capture is detected at block 336. A differentcandidate LV bipolar pair is selected at block 338, and the processreturns to block 314 to determine if anodal capture occurs with the newbipolar pair.

If threshold 1 for the candidate bipolar pair is closer to the controlthreshold, this evidence does not fully support the detection of anodalcapture based on measured CTs. Anodal capture may be reported assuspected but not confirmed at block 340. A clinician may choose toaccept the candidate bipolar pair for therapy delivery, or anothercandidate bipolar pair is selected at block 338.

In Table I, example capture threshold test results are listed for LVpacing electrode pairs. The control capture threshold is listed for eachLV electrode, LV1, LV2, LV3 and LV4, available on a quadripolar CS LVlead used as a cathode paired with an RV coil electrode as a “universal”anode for collecting control data. Note that the capture threshold forLV4-RVcoil is 8.1 V, considerably greater than the capture threshold forany of the other LV electrodes selected as cathodes.

The bipolar capture thresholds for each bipolar combination includingLV4 as the cathode (and LV1, LV2, or LV3 selected as the anode) is alsolisted. Note that the bipolar capture threshold for LV4 to LV1 pacing islow, 1.0 V. This capture threshold would be measured as the bipolarthreshold1 at block 328 when LV4 is selected as the candidate cathode.

The capture threshold for LV1 to LV4 is 0.8 V. This capture thresholdwould be measured as the test threshold2 at block 332, for the reversedpolarity of the candidate LV bipole. The capture threshold1 (LV4 to LV1)is much less than the control capture threshold (LV4 to LVcoil), and isnearer test threshold2 (LV1-LV4). This result suggests that capture isnot occurring at LV4, which was associated with a high capture thresholdwhen paired with the RV coil electrode. Instead, anodal capture isprobably occurring at LV1 when the LV4-LV1 bipole is selected.

TABLE I Capture thresholds measured during LV pacing. Pacing Capturevector Threshold (V) LV1 to RV 0.6 coil LV2 to RV 1.1 coil LV3 to RV 2.0coil LV4 to RV 8.1 coil LV1 to LV2 0.7 LV1 to LV3 0.8 LV1 to LV4 0.8 LV4to LV1 1.0 LV4 to LV2 4.7 LV4 to LV3 9.2

Anodal capture thresholds will typically be significantly higher thancathodal capture thresholds. However, even if the threshold1 is not muchless than the control capture threshold or is closer to the controlthreshold than the test threshold 2, anodal capture may still beoccurring when the bipolar CT is much shorter than the control CT. Forexample simultaneous anodal and cathodal capture may be occurring whenthe bipolar CT does not approximately match the control CT but thecapture threshold data does not provide strong evidence for anodalcapture. Suspected anodal stimulation, in such cases, can be reported atblock 340. A clinician may decide whether to select a differentelectrode pair at block 338 or accept the tested bipole. In some cases,simultaneous anodal and cathodal capture may be acceptable, for examplebased on an analysis hemodynamic parameters.

FIG. 6 is a flow chart 400 of a method for discriminating between anodaland cathodal capture according to yet another alternative embodiment. Ananodal capture test is initiated at block 402. An electrode positionedalong or in the LV is selected as a candidate cathode at block 404 andused to deliver LV pacing pulses with a universal anode, which maypositioned away from the LV or along the LV as described above inconjunction with FIGS. 4B and 4C. In one embodiment, the universal anodeis a large electrode positioned away from the LV, such as a housingelectrode along the IMD housing or an RV coil electrode.

At block 406, a control LV evoked response (ER) measurement is made. Thecontrol ER signal is measured from an EGM signal obtained at the pacingcathode electrode and another sensing electrode. An ER measurement mayrelate to a time interval from the pacing pulse to a point along the ERsignal, a measurement of a morphological feature of the ER signal, or atemplate of the morphology of the ER signal waveform. ER sensing isgenerally disclosed in U.S. Pat. No. 7,123,963 (Sawchuk et al.), herebyincorporated herein by reference in its entirety. The ER signal isdigitized and digital analysis of the waveform is performed to obtain atime interval or morphology-related measurement. An ER morphologymeasurement may be made using any waveform analysis method. A waveletmorphology analysis method that may be implemented to perform an ERmorphology measurement at block 406 is generally described in U.S. Pat.No. 6,393,316 (Gillberg, et al.), hereby incorporated herein byreference in its entirety. The control ER measurement is stored at block406 for future comparison for discriminating anodal and cathodalcapture.

At block 408, an LV bipolar pacing pair is selected using the candidateLV cathode electrode and any available LV anode. Bipolar LV pacing isdelivered using the selected bipole. At block 410, the ER measurement isrepeated during the LV bipolar pacing. At block 411, the LV anode usedduring bipolar pacing is switched to a cathode and LV pacing isdelivered using the “universal” anode that was also used for measuringthe control ER. A test ER measurement is performed when the candidatebipole anode is switched to a cathode to obtain a test ER measurementcorresponding to capture occurring at the anode site of the candidate LVbipole.

At block 412, the bipolar ER measurement is compared to the control ERmeasurement and the test ER measurement. If the bipolar ER measurementis closer to the control ER measurement, cathodal capture is detected atblock 420. The device may be programmed to automatically pace in the LVusing the candidate LV bipolar pair.

If the bipolar ER measurement is closer to the test ER measurement,anodal capture is suspected and a warning is generated at block 414. Inone embodiment, a morphology matching score is computed between thebipolar ER morphology and the control ER morphology. A second morphologymatching score is computed between the bipolar ER morphology and thetest ER morphology. If the morphology matching score corresponding tothe control ER morphology is higher than the matching scorecorresponding to the test ER morphology, cathodal capture is detected.If the morphology matching score corresponding to the test ER morphologyis higher, anodal capture is detected.

If anodal capture is detected, other available LV electrodes may beselected as anodes with the same candidate LV cathode electrode asindicated at blocks 416 and 418 to identify a bipolar pair that does notresult in anodal stimulation. If all available LV anodes have beentested with the candidate cathode, a new candidate cathode may beselected at block 404.

The use of an ER measurement may be used alone or in any combinationwith one or both of the CT measurements and capture thresholdmeasurements described above for discriminating between anodal andcathodal capture. For example, an ER measurement may be used to confirmthe suspected presence of anodal capture based on CT measurements.

FIG. 7 is a flow chart 500 of a method for performing anodal captureanalysis and reporting according to one embodiment. In theabove-described embodiments, it is assumed that LV pacing delivered toobtain control measurements does not result in anodal capture. In otherwords it is assumed that anodal capture does not occur at a “universal”anode used to measure control responses and sometimes test responses topacing pulses. In some cases, anodal capture may be occurring at theuniversal anode, when located in the same or another heart chamber. Thisanodal capture will produce confounding results when discriminatingbetween anodal and cathodal capture during bipolar pacing in a heartchamber.

When the universal anode is selected away from the heart, such as ahousing electrode along the IMD housing or a subcutaneous large surfacearea electrode, capture at the universal anode can be avoided. When inthe heart, such as the RV, anodal capture without cathodal capture inthe LV or a combination of anodal and cathodal capture simultaneously inboth the RV and LV could occur. The method shown in flow chart 500 isused to test all available bipole combinations in a heart chamber anddiscriminate between anodal and cathodal capture, even when a controlmeasurement may represent anodal capture at the universal anode ratherthan capture at the candidate cathode. A report can be generatedindicating under what conditions anodal capture is detected or suspectedproviding a clinician with valuable information for selecting pacingvectors for achieving a desired therapeutic benefit.

At block 502, an anodal capture test is started. The test may beinitiated upon user command, upon implant detection or other triggeringevent. In some embodiments, the anodal capture evaluation is performedin conjunction with capture threshold testing such that both capturethresholds and any detected or suspected anodal capture may be reportedtogether. As such, at block 504, capture thresholds are measured foreach candidate cathode, paired with a universal anode to obtain controlcapture thresholds and in candidate bipolar pairs with each availableanode to obtain bipolar capture thresholds with all possible bipoles.

At block 506, the associated CTs for each pacing combination aremeasured during the capture threshold tests. For example, during LVpacing, the control CT is measured for each candidate LV cathode pairedwith the universal anode, e.g. the RV coil electrode. These control CTsare stored for each respective candidate cathode. Additionally, duringcapture threshold measurements for each candidate bipole, an associatedbipolar CT is measured. Each candidate LV cathode is paired with allavailable LV anode electrodes one at a time such that all possiblebipolar LV pacing vectors are used to deliver bipolar LV pacing andmeasure a corresponding bipolar CT at a distant sensing site.

At block 508, a candidate cathode is selected for evaluation forpotential anodal capture. The control CT measured for the candidatecathode (during pacing with the universal anode) is compared to aminimum expected CT at block 510. A physiological minimum CT ispreviously established and stored in IMD memory. An established minimumCT and may be based on clinical data or individual patient data as anexpected conduction time from the cathode pacing site to a distantbipole sensing a local R-wave. The distant bipole sensing a conducteddepolarization signal typically but not necessarily including theuniversal anode as one of the sensing electrodes. The sensing bipole maybe in the paced heart chamber or the opposite heart chamber. In oneembodiment, the control CT is measured using a sensing electrode pair inthe RV, e.g. RV tip to RV ring. A minimum CT from LV pace to RV sense isdefined as approximately 60 ms. If the control CT measured for thecandidate cathode paired with a universal anode positioned in the RV isless than the minimum CT, anodal capture is likely to be occurring inthe RV because conduction from the LV to the RV is not expected to occurfaster than the minimum CT.

If the control CT is not less than a minimum physiological CT (negativeresult at decision block 510), cathodal capture is likely occurring inthe LV during pacing using the universal anode. This result of thecontrol CT being greater than the minimum CT indicates that the controlCT is a reliable measure for use in discriminating anodal capture duringbipolar pacing. At block 511 the control CT is classified as normal, andat block 512 each bipolar CT measured for the cathode under evaluationis compared to the normal control CT.

If all bipolar CTs measured for the candidate cathode are within apreviously established threshold range of the control CT at block 512,all bipolar pacing vectors using the candidate cathode under evaluationare labeled as having normal CTs at block 514. The threshold range usedat block 512 may be defined, for example, as approximately 10 ms. The“normal” CTs that are within a threshold range of the control CT arelikely to be associated with cathodal capture. If additional candidatecathodes remain to be evaluated, as determined at block 516, the nextcandidate cathode is selected for evaluation at block 508.

Returning to block 512, if any bipolar CT is outside a threshold rangeof the control CT, that bipolar CT is classified as abnormal at block528. Any bipolar CTs using the candidate cathode that are within thethreshold range of the control CT are classified as normal at block 528.As such, for a given cathode electrode, some bipolar CTs may beclassified as abnormal and some may be classified as normal dependingwhether the associated CT falls within a predefined range of the normalcontrol CT.

At block 530, a mean CT is computed for each electrode being tested. Amean CT is computed using only CTs classified as normal for a givencathode. When arriving at block 530 from block 528, the normal CTsinclude a normal control CT and any bipolar CTs classified as normal atblock 528.

At block 532, a bipolar CT classified as abnormal is compared to themean CT for the candidate cathode and to the mean CT computed for theelectrode used as an anode in the candidate bipole, when the abnormalbipolar CT was measured. The mean CT computed for the anode associatedwith an abnormal CT is computed from all bipolar and control CTsmeasured for the anode, which switched to a cathode polarity, andclassified as normal CTs. If an abnormal bipolar CT is closer to themean CT computed for the candidate bipole anode, as determined at block534, a warning of anodal capture for the associated bipole is generatedat block 536. If all of the abnormal CTs are closer to the mean CTcomputed for the candidate cathode, then no warning of anodal capture isgenerated. The process advances to block 516.

Returning to block 510, if a control CT is less than the minimum CT, awarning of anodal capture is generated at block 518 for the candidatecathode and universal anode pair. The control CT is classified asabnormal for the candidate cathode under evaluation. In this case, thecontrol CT is not deemed reliable for discriminating between anodal andcathodal capture during bipolar pacing.

In this situation, each bipolar CT measured for the candidate cathode iscompared to each of the other bipolar CTs measured for that cathode atblock 520. If none are within a previously established range of eachother, for example, within approximately 10 ms of each other, the all ofthe bipolar CTs measured for the candidate cathode being evaluated arelabeled “abnormal” at block 522. A warning of anodal capture using thecandidate cathode is generated. The process proceeds to block 516 toevaluate the next candidate cathode.

If any bipolar CTs are within a predefined range of another bipolar CTfor the same candidate cathode as determined at decision block 520, allbipolar CTs within a threshold range of another bipolar CT areclassified as normal at block 524. All “outliers” that are not within anestablished threshold range of at least one other bipolar CT areclassified as abnormal CTs at block 524.

At block 530, a mean CT is computed for each electrode using all normalCTs measured for the given electrode. When arriving at block 530 fromblock 524, the control CT is excluded from computing a mean CT for thecandidate cathode because the control CT has been classified asabnormal. All bipolar CTs falling within an established range of atleast one other bipolar CT and therefore classified as normal are usedto compute the mean CT for a given electrode.

Any bipolar CTs classified as abnormal for the candidate cathode arecompared to the mean CT for the candidate cathode at block 532. Anabnormal bipolar CT is additionally compared to a mean CT computed forthe electrode being used as the anode in the candidate bipole resultingin the abnormal CT. If an abnormal bipolar CT is closer to the mean CTdetermined for the electrode now being used as an anode, anodal captureis likely occurring. If the abnormal CT is closer to the mean CTdetermined for the candidate cathode, cathodal capture is likely to beoccurring. In this way, if the cathode being evaluated results incathodal capture for some lead vectors, these can be identified asbipolar vectors having close CT measurements, whereas outliers can beidentified as “abnormal” and separated from normal bipolar CTmeasurements, even when the control CT measurement is classified asabnormal.

If there are any bipolar CT measurements that are closer to the mean CTfor the anode electrode than to the mean CT for the cathode electrode asdetermined at decision block 534, then a warning of anodal capture forthe associated bipole(s) is generated at block 536. If all abnormal CTsare closer to the mean CT computed for the candidate cathode than themean CT for the associated anode, no warning of anodal capture isgenerated. The process returns to block 516. In this way, anodal captureis detected and discriminated from cathodal capture during bipolarpacing even when a control response using a universal anode results insuspected anodal capture.

After evaluating all candidate cathodes, an anodal capture report isgenerated at block 530. The report may be an on-screen display,printable report or other format including text, tables, or graphs ofdata determined during the anodal capture test. The anodal capturereport may additionally include capture threshold data and/or evokedresponse measurement data. The anodal capture report will warn of anodalcapture for any cathode found to have all abnormal CTs associated withevery possible bipolar pacing pair tested. The report may further warnof possible anodal capture for any specific bipolar vectors found tohave abnormal CTs closer to a mean CT computed for the anode of thebipolar vector than to a mean CT computed for the cathode of the bipolarvector. Any candidate cathode having all normal CTs for every bipolarvector tested may be indicated as a recommended cathode for therapydelivery and avoidance of anodal capture.

FIG. 8 is a schematic diagram of a configuration 600 for detectinganodal capture during bipolar pacing using evoked response sensing.Bipolar pacing is delivered along a vector 610 between a candidatecathode electrode 601 and candidate anode electrode 603. ER sensing isperformed at both the cathode 601 and the anode 603 using a thirdindifferent electrode 602. In other embodiments, ER sensing performed atthe cathode 601 and at the anode 603 may use separate indifferentelectrodes for sensing the local ER at the respective electrode 601 or603, rather than a shared indifferent electrode as shown here.

FIG. 9 is a flow chart 700 of a method for detecting anodal captureduring bipolar pacing using ER sensing at both the candidate cathode andanode as generally depicted in the configuration of FIG. 8. At 702, theanodal capture test is initiated. A candidate bipole is selected atblock 704, and bipolar pacing is delivered at block 706. An ER is sensedat both the cathode electrode and the anode electrode at block 708. Atime interval to the ER signals is determined at block 710. The timingof the evoked responses relative to a delivered pacing pulse can be thetiming of a sense amplifier output or the timing of a feature in thedigitized EGM signal, such as the maximum amplitude or slope or otherfeatures listed previously.

At block 712, the anodal ER time is compared to the cathodal ER time. Ifan ER is sensed at the anode earlier than at the cathode, anodal captureis detected at block 720. If the ER signals are sensed substantiallysimultaneously, as determined at block 714, simultaneous anodal andcathodal capture is detected at block 718.

If the ER is sensed earlier at the cathode than at the anode, cathodalcapture is detected at block 716. Anodal capture is not detected. Thecandidate bipole may be selected as a bipolar pacing pair for therapydelivery.

If simultaneous anodal and cathodal capture is detected and/or if anodalcapture is detected, the anodal and cathodal capture thresholds may bedetermined at block 722 and 724, respectively. In one embodiment, thepacing pulse amplitude is adjusted until an ER signal within apredetermined time interval of the pacing pulse disappears. The lowestpacing pulse amplitude at which the ER occurs at a given electrodewithin a predetermined time interval is determined as the capturethreshold.

If the cathodal capture threshold is within a narrow range of the anodalcapture threshold, such as within a pacing safety margin, as determinedat block 726, an anodal capture warning is withheld at block 730. Sincepacing will generally occur at a pacing safety margin above a capturethreshold, anodal and cathodal capture thresholds falling within asafety margin of each other will generally result in simultaneous anodaland cathodal capture. Simultaneous anodal and cathodal capture may beacceptable in many pacing therapies making an anodal capture warningunnecessary.

If the capture threshold is substantially higher at the cathode than atthe anode, anodal stimulation only may occur for a range of pacing pulseamplitudes. An anodal capture warning is generated at block 728 if thecathodal capture threshold is not within a predetermined narrow range,for example within a pacing safety margin, of the anodal capturethresholds as determined at block 726.

FIG. 10 is a flow chart 800 of a method for detecting and discriminatinganodal, cathodal and simultaneous anodal and cathodal capture duringbipolar pacing. At block 802 the anodal capture test is started for aselected bipole and begins by performing an analysis of CT at block 804by measuring a control, bipolar and test CT as described previously. Ifanodal capture is not suspected based on the CT measurements, asdetermined at decision block 806, cathodal capture is detected at block810.

If anodal capture is suspected at block 806, the ER is measured at theanode and the cathode of the candidate bipole during bipolar pacing atblock 812. If an ER is sensed earlier at the anode than at the cathode,as determined at decision block 814, the suspected anodal capture isconfirmed and a warning is generated at block 818. If the ER does notoccur earlier at the anode than at the cathode, an abnormal CT may bereported at block 816. The ER measurements do not support anodal capturedetection, but an unexpected bipolar CT may be reported to allow aclinician to further evaluate the candidate bipole or alternative pacingbipoles.

In the flow charts presented herein, it is recognized that all blocksshown may not be performed in some embodiments or may be performed in adifferent order than the order shown. For example, in some embodiments,CT, capture threshold data, and/or ER data, alone or in any combination,may be measured for all available electrode vectors to allow an optimalbipolar pacing vector to be selected. In other embodiments, anodalcapture analysis data may be acquired for a desired bipolar vector andif anodal capture is not suspected based on the anodal capture analysisdata, the bipolar vector may be selected without further testing. Thevarious measurements described herein for discriminating between anodaland cathodal capture, such as CT measurements, capture thresholdmeasurements, and ER time or morphology measurements may be performed inany combination.

Thus, an apparatus and method for discriminating between anodal andcathodal capture during bipolar pacing have been presented in theforegoing description with reference to specific embodiments. It isappreciated that various modifications to the referenced embodiments maybe made without departing from the scope of the disclosure as set forthin the following claims.

The invention claimed is:
 1. A method for detecting anodal cardiaccapture during bipolar electrical stimulation, the method comprising:delivering a first pacing pulse using a first bipole comprising a firstcathode and a first anode both positioned along a heart chamber;delivering a second pacing pulse using the first cathode and a secondanode; measuring a first response to the first pacing pulse; measuring asecond response to the second pacing pulse; detecting anodal capture ofthe heart chamber by the first pacing pulse at the first anode inresponse to a first difference between the first response and the secondresponse; switching the polarity of the first anode to a cathode;delivering a third pacing pulse between the first anode switched to thecathode polarity and the second anode; measuring a third response to thethird pacing pulse; and detecting anodal capture in response to thefirst difference being greater than a second difference between thefirst response and the third response.
 2. The method of claim 1, whereinthe first bipole is positioned along a heart chamber and delivering thesecond pacing pulse comprises selecting the second anode as an electrodepositioned away from the heart chamber and delivering the second pacingpulse as a unipolar pacing pulse.
 3. The method of claim 1, whereinmeasuring the responses to the first and second pacing pulsesrespectively comprises measuring a first conduction time between thefirst pacing pulse and a subsequent depolarization sensed at a sensingelectrode positioned a distance from the first bipole and a secondconduction time between the second pacing pulse and a subsequentdepolarization sensed at the sensing electrode.
 4. A method fordetecting anodal cardiac capture during bipolar electrical stimulation,the method comprising: delivering a first pacing pulse using a firstbipole comprising a first cathode and a first anode both positionedalong a heart chamber; delivering a second pacing pulse using the firstcathode and a second anode; measuring a first response to the firstpacing pulse; measuring a second response to the second pacing pulse;detecting anodal capture of the heart chamber by the first pacing pulseat the first anode in response to a first difference between the firstresponse and the second response; measuring a first capture thresholdcorresponding to the first bipole; measuring a second capture thresholdcorresponding to the first cathode and the second anode; delivering thefirst pacing pulse at a fixed increment above the first capturethreshold and delivering the second pacing pulse at the fixed incrementabove the second capture threshold, wherein measuring the responses tothe first and second pacing pulses respectively comprises measuring afirst conduction time between the first pacing pulse and a subsequentdepolarization sensed at a sensing electrode positioned a distance fromthe first bipole and a second conduction time between the second pacingpulse and a subsequent depolarization sensed at the sensing electrode.5. The method of claim 1 wherein delivering the third pacing pulsecomprises selecting the first anode and the second anode from aplurality of electrodes positioned along a single heart chamber.
 6. Themethod of claim 1 wherein the first bipole is positioned along a heartchamber and delivering the second pacing pulse comprises selecting thesecond anode as an electrode positioned away from the heart chamber. 7.The method of claim 1, wherein measuring the first response to the firstpacing pulse further comprises delivering at least one additional pacingpulse to determine a first capture threshold corresponding to the firstbipole, measuring the second response to the second pacing pulse furthercomprises delivering at least one additional pacing pulse to determine asecond capture threshold corresponding to the first cathode and thesecond anode, wherein detecting anodal capture further comprisesdetermining a first capture threshold difference between the firstcapture threshold and the second capture threshold.
 8. The method ofclaim 7, further comprising measuring the first capture threshold andthe second capture threshold in response to the first difference beinggreater than a threshold.
 9. A method for detecting anodal cardiaccapture during bipolar electrical stimulation, the method comprising:delivering a first pacing pulse using a first bipole comprising a firstcathode and a first anode both positioned along a heart chamber;delivering a second pacing pulse using the first cathode and a secondanode; measuring a first response to the first pacing pulse; measuring asecond response to the second pacing pulse; detecting anodal capture ofthe heart chamber by the first pacing pulse at the first anode inresponse to a first difference between the first response and the secondresponse; switching the polarity of the first anode to a cathode;switching the polarity of the first cathode to an anode; and measuring athird capture threshold corresponding to a second bipole comprising thefirst cathode switched to the anode polarity and the first anodeswitched to the cathode polarity; wherein detecting anodal capturefurther comprises detecting anodal capture in response to the firstcapture threshold difference being greater than a second capturethreshold difference between the first capture threshold and the thirdcapture threshold, wherein measuring the first response to the firstpacing pulse further comprises delivering at least one additional pacingpulse to determine a first capture threshold corresponding to the firstbipole, measuring the second response to the second pacing pulse furthercomprises delivering at least one additional pacing pulse to determine asecond capture threshold corresponding to the first cathode and thesecond anode, and wherein detecting anodal capture further comprisesdetermining a first capture threshold difference between the firstcapture threshold and the second capture threshold.
 10. The method ofclaim 1, wherein measuring the first response comprises measuring afirst evoked response subsequent to the first pacing pulse and measuringthe second response comprises measuring a second evoked responsesubsequent to the second pacing pulse.
 11. The method of claim 10,wherein measuring the first and second evoked responses comprises atleast one of measuring a time interval from the respective first pacingpulse and the second pacing pulse to the sensed first evoked responseand the second evoked response and determining a morphological featureof the first and second evoked responses.
 12. A method for detectinganodal cardiac capture during bipolar electrical stimulation, the methodcomprising: delivering a first pacing pulse using a first bipolecomprising a first cathode and a first anode both positioned along aheart chamber; delivering a second pacing pulse using the first cathodeand a second anode; measuring a first response to the first pacingpulse; measuring a second response to the second pacing pulse; detectinganodal capture of the heart chamber by the first pacing pulse at thefirst anode in response to a first difference between the first responseand the second response; measuring a time to a first evoked responsesensed at the first cathode and measuring a time to a second evokedresponse sensed at the first anode; responsive to the second evokedresponse occurring earlier than the first evoked response performing acapture threshold test to determine an anodal capture threshold and acathodal capture threshold; establishing a pacing safety margin; andgenerating a warning of anodal capture in response to the cathodalcapture threshold being more than the pacing safety margin greater thanthe anodal capture threshold.
 13. A medical device for detecting anodalcardiac capture, comprising: a plurality of electrodes for sensingcardiac signals and delivering cardiac pacing pulses; a therapy deliverymodule for delivering cardiac pacing pulses to a patient's heart via theplurality of electrodes; cardiac signal sensing circuitry for receivingsignals from the plurality of electrodes; and a controller configuredto: control the therapy delivery module to deliver a first pacing pulseusing a first bipole comprising a first cathode and a first anode bothpositioned along a heart chamber and deliver a second pacing pulse usingthe first cathode and a second anode; measure a first response of areceived cardiac signal to the first pacing pulse; measure a secondresponse of the received cardiac signal to the second pacing pulse; anddetect anodal capture of the heart chamber by the first pacing pulse atthe first anode in response to a first difference between the firstresponse and the second response, wherein the controller is furtherconfigured to: switch the polarity of the first anode to a cathode;cause the therapy delivery module to deliver a third pacing pulsebetween the first anode switched to the cathode polarity and the secondanode; measure a third response to the third pacing pulse; and detectanodal capture in response to the first difference being greater than asecond difference between the first response and the third response. 14.The device of claim 13, wherein the first bipole is positioned along aheart chamber, the controller further configured to cause the therapydelivery module to deliver the second pacing pulse by selecting thesecond anode as an electrode positioned away from the heart chamber. 15.The device of claim 13, wherein the controller is configured to measurethe responses to the first and second pacing pulses respectively bymeasuring a first conduction time between the first pacing pulse and asubsequent depolarization sensed at a sensing electrode positioned adistance from the first bipole and a second conduction time between thesecond pacing pulse and a subsequent depolarization sensed at thesensing electrode.
 16. A medical device for detecting anodal cardiaccapture, comprising: a plurality of electrodes for sensing cardiacsignals and delivering cardiac pacing pulses; a therapy delivery modulefor delivering cardiac pacing pulses to a patient's heart via theplurality of electrodes; cardiac signal sensing circuitry for receivingsignals from the plurality of electrodes; and a controller configuredto: control the therapy delivery module to deliver a first pacing pulseusing a first bipole comprising a first cathode and a first anode bothpositioned along a heart chamber and deliver a second pacing pulse usingthe first cathode and a second anode; measure a first response of areceived cardiac signal to the first pacing pulse; measure a secondresponse of the received cardiac signal to the second pacing pulse; anddetect anodal capture of the heart chamber by the first pacing pulse atthe first anode in response to a first difference between the firstresponse and the second response, wherein the controller is furtherconfigured to: measure a first capture threshold corresponding to thefirst bipole; measure a second capture threshold corresponding to thefirst cathode and the second anode; and cause the therapy deliverymodule to deliver the first pacing pulse at a fixed increment above thefirst capture threshold and delivering the second pacing pulse at thefixed increment above the second capture threshold, wherein thecontroller is configured to measure the responses to the first andsecond pacing pulses respectively by measuring a first conduction timebetween the first pacing pulse and a subsequent depolarization sensed ata sensing electrode positioned a distance from the first bipole and asecond conduction time between the second pacing pulse and a subsequentdepolarization sensed at the sensing electrode.
 17. The device of claim13 wherein the controller is further configured to cause the therapydelivery module to deliver the third pacing pulse by selecting the firstanode and the second anode from a plurality of electrodes positionedalong a single heart chamber.
 18. The device of claim 13 wherein thefirst bipole is positioned along a heart chamber and the therapydelivery module is controlled by the controller to deliver the secondpacing pulse by selecting the second anode as an electrode positionedaway from the heart chamber.
 19. The device of claim 13, wherein thecontroller is further configured to control the therapy delivery moduleto deliver at least one additional first pacing pulse and to determine afirst capture threshold corresponding to the first bipole, control thetherapy delivery module to deliver at least one additional second pacingpulse and to determine a second capture threshold corresponding to thefirst cathode and the second anode, and the controller furtherconfigured to determine a first capture threshold difference between thefirst capture threshold and the second capture threshold, whereindetecting anodal capture comprises detecting anodal capture in responseto the first capture threshold difference.
 20. The device of claim 19,wherein the controller is configured to measure the first capturethreshold and the second capture threshold in response to the firstdifference being greater than a threshold.
 21. A medical device fordetecting anodal cardiac capture, comprising: a plurality of electrodesfor sensing cardiac signals and delivering cardiac pacing pulses; atherapy delivery module for delivering cardiac pacing pulses to apatient's heart via the plurality of electrodes; cardiac signal sensingcircuitry for receiving signals from the plurality of electrodes; and acontroller configured to: control the therapy delivery module to delivera first pacing pulse using a first bipole comprising a first cathode anda first anode both positioned along a heart chamber and deliver a secondpacing pulse using the first cathode and a second anode; measure a firstresponse of a received cardiac signal to the first pacing pulse; measurea second response of the received cardiac signal to the second pacingpulse; detect anodal capture of the heart chamber by the first pacingpulse at the first anode in response to a first difference between thefirst response and the second response; control the therapy deliverymodule to deliver at least one additional first pacing pulse and todetermine a first capture threshold corresponding to the first bipole,control the therapy delivery module to deliver at least one additionalsecond pacing pulse and to determine a second capture thresholdcorresponding to the first cathode and the second anode, and thecontroller further configured to determine a first capture thresholddifference between the first capture threshold and the second capturethreshold, wherein detecting anodal capture comprises detecting anodalcapture in response to the first capture threshold difference, whereinthe controller is further configured to: switch the polarity of thefirst anode to a cathode; switch the polarity of the first cathode to ananode; and measure a third capture threshold corresponding to a secondbipole comprising the first cathode switched to the anode polarity andthe first anode switched to the cathode polarity wherein detectinganodal capture further comprises detecting anodal capture in response tothe first capture threshold difference being greater than a secondcapture threshold difference between the first capture threshold and thethird capture threshold.
 22. The device of claim 13, wherein thecontroller is configured to measure the first response by measuring afirst evoked response subsequent to the first pacing pulse and measurethe second response by measuring a second evoked response subsequent tothe second pacing pulse.
 23. The device of claim 22, wherein measuringthe first and second evoked responses comprises at least one ofmeasuring a time interval from the respective first pacing pulse and thesecond pacing pulse to the respective sensed first evoked response andthe second evoked response, and determining a morphological feature ofthe respective first and second evoked responses.
 24. A medical devicefor detecting anodal cardiac capture, comprising: a plurality ofelectrodes for sensing cardiac signals and delivering cardiac pacingpulses; a therapy delivery module for delivering cardiac pacing pulsesto a patient's heart via the plurality of electrodes; cardiac signalsensing circuitry for receiving signals from the plurality ofelectrodes; and a controller configured to: control the therapy deliverymodule to deliver a first pacing pulse using a first bipole comprising afirst cathode and a first anode both positioned along a heart chamberand deliver a second pacing pulse using the first cathode and a secondanode; measure a first response of a received cardiac signal to thefirst pacing pulse; measure a second response of the received cardiacsignal to the second pacing pulse; and detect anodal capture of theheart chamber by the first pacing pulse at the first anode in responseto a first difference between the first response and the secondresponse, wherein the controller is further configured to measure a timeto a first evoked response sensed at the first cathode and measure atime to a second evoked response sensed at the first anode; responsiveto the second evoked response occurring earlier than the first evokedresponse perform a capture threshold test to determine an anodal capturethreshold and a cathodal capture threshold; establish a pacing safetymargin; and generate a warning of anodal capture in response to thecathodal capture threshold being more than the pacing safety margingreater than the anodal capture threshold.
 25. A non-transitorycomputer-readable medium storing a set of instructions which whenimplemented in a medical device cause the device to perform a method fordetecting anodal capture, the method comprising: delivering a firstpacing pulse using a first bipole comprising a first cathode and a firstanode both positioned along a heart chamber; delivering a second pacingpulse using the first cathode and a second anode; measuring a firstresponse to the first pacing pulse; measuring a second response to thesecond pacing pulse; detecting anodal capture of the heart chamber bythe first pacing pulse at the first anode in response to a firstdifference between the first response and the second response; switchingthe polarity of the first anode to a cathode; delivering a third pacingpulse between the first anode switched to the cathode polarity and thesecond anode; measuring a third response to the third pacing pulse; anddetecting anodal capture in response to the first difference beinggreater than a second difference between the first response and thethird response.
 26. The method of claim 1, wherein the second anode is acoil electrode.